KR102040583B1 - Methods, plants and molds for forming slabs of aggregates - Google Patents

Abstract

The method for the preparation of a mold 10 intended to form a slab from a mixture of aggregates comprises a sheet of PVA-based plastic material 15 to form a surface for subsequent contact with the mixture introduced into the mold to form the slab. ) Is deposited on the mold surface, at least in some regions, a layer 14 of flow agent comprising PVA in solution is sandwiched between the sheet 15 and the mold surface. Also described is a method and method for performing the production of slabs.

Description

Methods, plants and molds for forming slabs of aggregates

The present invention relates to a method and a plant for preparing a mold and for forming a slab of agglomerates, for example agglomerates of stone material particles or powders bonded with a cured resin. The invention also relates to a method for the production of molds and slabs prepared using such a method.

In the production of slabs of agglomerates, it is necessary to separate the mold from the slab thus formed after the material for forming the slab has been injected into the mold and cured, preferably after any vacuum vibrocompression.

The mold is preferably made in the form of a flexible sheath of elastomeric material, such as synthetic rubber, and generally comprises a bottom sheet of rubberized fabric and a top closure sheet of rubberized fabric in the form of a tray with edges. It is usually configured. This mold, once filled with the aggregate mixture, then receives the appropriate vacuum vibration compression force from the outside to form the slab.

Over time, in an attempt to prevent the cured sheet from adhering to the mold, particularly the top rubber sheet of the bottom rubber sheet and the elastomer mold, and to protect the rubber sheet from attack by the resin binder with any associated solvents. Many solutions have been developed.

For example, in IT1311857 it has been proposed to pre-spray the surface of the rubberized sheet with a fluid separation / protectant essentially formed by a solution based on PVA (polyvinyl alcohol) before injecting the mixture into the tray.

After the separating agent has dried, a thin solid and elastic film is thus formed which adheres properly to the surface of the rubberized sheet. The adhesion of the PVA film to the rubberized sheet, although weakened, prevents the formation of undulations or wrinkles on the film and thus on the surface of the slab during the vibrational compression step. Such films provide protection for the sheets of the mold from solvents such as resins and styrene and also allow separation of the sheets from the cured slab at the end of the high temperature catalytic process.

This occurs in both the rubberized sheet of the bottom into which the mixture is injected and the top rubberized sheet covering the mixture.

Instead, the PVA film is firmly attached to the cured slab and extracted from the mold with the slab. During the subsequent process for wet grinding and sizing the slab, the film is dissolved by process water and discharged with the wet process sludge.

The PVA film can be mechanically peeled from the slab instead of dissolved in water if desired.

This solution is effective but has a number of disadvantages associated with the fact that the protective / separating agent is generally fluid because it must be applied by spraying means and then dried.

In order to obtain a sufficiently compact layer, a relatively high amount of fluid, for example about 200 g / m², is typically applied to obtain a film of about 30 to 40 g / m² after drying.

However, there is a real risk that the agent may not be sprayed uniformly over the entire mold or bubbles or voids may form, which, after drying, has the risk that the solvent can pass through and eventually damage the elastomer mold. Holes in the film can be created.

However, it has also been proposed to spray fluid agents at relatively high temperatures (eg, about 50 ° C.) to ensure sufficient fluidity, but the water present therein can be excessively evaporated during application and As a result, there is a risk of loss of fluid properties required for the correct application of the layer.

However, it is also necessary to periodically clean the nozzles, which operation is by no means simple in terms of the sticky nature of the solution to ensure uniform spraying of the layer.

In addition, the large amount of solution required for spraying requires time and attention during drying to remove all the significant amount of water in the solution and at the same time keep the thickness of the sprayed layer sufficiently uniform.

Finally, it should be considered that after spraying, the drying of the PVA solution must be carried out in a suitable drying oven to obtain a sufficiently fast drying before the mixture can be injected into the mold. However, oven drying is a delicate process that must be performed carefully to prevent boiling and / or bubbles and the formation of pitting.

The presence of the oven also results in an increase in the overall dimensions and costs of the plant and a significant increase in the amount of electrical energy used during the process. The oven speeds up the drying process, but nevertheless complete drying requires a certain amount of time.

For this reason, another solution has been developed, which envisages protecting the mold using a solid sheet of suitable material which is placed directly on the bottom and wall of the bottom mold before injection into the mixture.

The sheet should be chosen to have the necessary properties for use in the mold as a means to protect and facilitate separation of the mold from the slab. For example, it should be impermeable to organic vapors, in particular styrene, impermeable to liquid resins, resistant to catalyst temperatures of the resin, and resistant at high temperatures to solvents and chemical vapors that develop during the slab production process.

Thus, sheets of plastic material (polypropylene or PET or PVA) have been devised; This is combined with a paper sheet having a total gram weight of about 40 to 250 g / m² if necessary.

After the layers of the mixture have cured, the cured slabs thus obtained are extracted from the mold along with the sheets that remain attached thereto. The sheet must then be removed from the slab.

Once made with PVA the sheet can simply be dissolved in water at room temperature; Otherwise it must be removed and removed in solid form, ie mechanically removed from the slab.

US2004 / 169303 describes an example of the use of a sheet of water soluble plastic material. This procedure is also effective, but hardening by forming reliefs or creases or folds that penetrate into the layers of the mixture during vibrational compression of the mixture inside the mold because the protective sheet simply sits on the rubberized sheet and does not adhere to it. The disadvantage is that it can remain in the finished slab.

Thus, during the sizing and polishing of the slab, it is necessary to mechanically remove any traces of paper or plastic film that has penetrated the slab. Due to the paper and / or plastic film penetrating the mixture, it is clear that in some cases, excessive thickness of the material, which can also be very large, must be removed. Nevertheless, even in the case of PVA that is dissolved in water, it is necessary to remove the material layer of the slab sufficient to ensure the disappearance of defects generated in the slab after capture of the sheet in the mixture.

Thus, this requires the creation of thicker slabs on the one hand to obtain a suitable extra thickness to be removed, and on the other hand, subsequent sizing that allows for a greater depth of processing, resulting in paper trapped in the slab and And / or PVA or polypropylene may be removed to avoid the resulting defects.

If this procedure is not adopted, it is required to treat low quality slabs.

It is a general object of the present invention to provide a method, a plant and a mold for the production of slabs of agglomerates which, among other things, can overcome the above-mentioned disadvantages of the prior art and can obtain a slab of satisfactory quality in a fast manner.

In view of this object, the idea according to the invention is to provide a method for the production of slabs from a mixture of agglomerates, which method comprises preparing a mold intended to form a slab from a mixture of agglomerates, which is introduced into the mold. Laminating at least one sheet of PVA-based plastic material over the surface of the mold to form with the slab a surface for subsequent contact with the mixture to be prepared, the fluid agent comprising a PVA in solution. The layer is sandwiched between at least some areas of the sheet and the mold surfaces.

Also according to the invention, the idea is also to provide a method for the production of slabs of aggregates, which method comprises the steps of preparing a mold using the method described above, introducing a mixture of aggregates into a mold to form a slab. Making a step; Preferably forming a slab by vacuum vibration compression; Performing a curing process of the mixture contained in the mold to consolidate the slab; Extracting the slab cured with the sheet from the mold; Removing the sheet from the slab. Removal may advantageously be carried out by simple dissolution.

According to the invention, a further idea is also to provide a plant for performing the steps according to the method of the preceding claims, which, in turn, provides for the application of a layer of fluid on at least some areas of the surface of the mold. A second station for lamination of a sheet of PVA-based plastic material on one station and a layer, and a conveyor, the conveyor moves between the first station and the second station, application of a layer of fluid and lamination of the sheet Or alternatively intended to sequentially deliver the mold to the first and second stations for displacement of the two stations over the fixed mold.

A further idea is to provide a mold intended to form a slab from a mixture of aggregates, which forms a slab between the base portion and at least some areas of the inner surface of the mold in which the layer of the sheet and the PVA-containing adhesive is present. A cover having a surface in the mold that is covered with at least one sheet of PVA-based plastic material to form a surface intended for subsequent contact with a mixture introduced into the mold. The mold may also include a suction duct intended to connect the space between the surfaces of the mold and the sheet to an external suction means for flattening or stretching the sheet to the mold surface by vacuum.

In order to more clearly illustrate the innovative principles and advantages of the present invention as compared to the prior art, a possible example of an embodiment to which this principle is applied will be described below with the aid of the accompanying drawings. In the drawings:
1 shows a schematic partial cross-sectional view of a mold prepared according to the invention.
2 shows a schematic measuring side view of a plant according to the invention.
3 shows a schematic of a larger scale of the station of the plant shown in FIG. 2.
4 shows a partial schematic cross sectional view along line IV-IV of FIG. 3.
FIG. 5 illustrates the operational steps of another station of the plant shown in FIG. 2.
6 and 7 illustrate the operational steps of the station of the plant shown in FIG. 3.
8 and 9 show an operational variant of the plant according to the invention.
10 shows a schematic plan view of a further process station of a plant according to the invention.
11 shows a schematic partial sectional view of the station according to FIG. 10.
12 shows a schematic of a larger scale of the details shown in FIG. 11.
FIG. 13 shows an enlarged schematic view of the details of the station shown in FIG. 11 in different operating positions.

Referring to the drawings, FIG. 1 shows a partial, schematic cross-sectional view of a mold according to the invention, generally indicated at 10.

The mold 10 is a mold made of synthetic rubber, which is flexible and preferably comprises a polymeric material, for example a silicone-type rubber, and comprises a bottom 11 and a top 12. A cloth or fabric reinforcement layer (not shown) made of a material that is substantially inelastic may also be provided on or within the outer or inner surface of the material forming the mold.

The bottom 11 is preferably realized in the form of a tray, ie with the raised peripheral edge 13, suitable for receiving a known mixture for forming a slab in a die cavity inside the mold. The mixture may be a known agglomerate mixture, for example agglomerates of stone particles or powder bound with a cured resin. Here, the term “die cavity” is understood to refer to a cavity of a mold that receives the mixture and is thus defined within the peripheral edge of the mold by the inner surface of the mold.

The top 12 is preferably substantially flat and forms a cover for closing the bottom. Advantageously, the mold may be of the type used for the known method of forming the slab by vacuum vibration compression, ie, if the mixture is injected and the mold is closed at the top, the mixture is with simultaneous application of vibration movement. It is delivered to a compression station undergoing a vacuum compression action. The compressed mixture is then sent to a station for curing the resin, preferably by heat application.

This type of mold is typically represented by the mechanical term "cis".

Before dispensing the mixture into the mold, the mold is prepared to facilitate subsequent extraction of the cured slab and to protect the mold surface that would otherwise be in contact with the mixture.

Preparation includes laminating a sheet 15 of PVA-based plastic material over the surface of the mold 10, the surface being the bottom 11 or top 12, and as described below, PVA ( A layer 14 of fluidizing agent (polyvinyl alcohol) is sandwiched between at least some area of the sheet 15 and the surface of the mold.

The sheet 15 forms a surface for subsequent contact with the mixture introduced into the mold to form the slab.

The PVA solution used as layer 14 may advantageously be formed by PVA in aqueous solution. Also preferably, the addition of glycerin can be considered. Such a solution may, for example, consist of about 1% to about 25% PVA, about 62% to about 95% water, and about 1% to about 10% glycerin (by weight percentage).

Additives such as known antifoams, leveling and settling additives may also be used.

For example, the following compositions were tested (values expressed in weight percent):

Although composition 1 is the preferred composition, compositions 2 to 7 can be used in accordance with the principles of the present invention. However, other compositions can be used.

It has proved particularly advantageous if a layer of flow agent is applied on the mold surface by mechanical contact of an applicator element immersed with the flow agent to the surface of the mold. This ensures application and the resulting formation of a thin uniform thickness of the fluid. Application can be carried out, for example, by rolling or sponge.

The average amount of flow agent applied may preferably be 2 to 10 g / m ² , and more preferably 4 to 6 g / m ² .

This ensures sufficient uniformity of coverage without using excessive amounts of flow agent which should have a small thickness (preferably less than 10 μm), thereby ensuring proper adhesion of the solid PVA film to the surface of the mold while at the same time Avoid the risk of solubilization and damage.

However, application by spraying can also be used, although it is difficult to perform in view of very small thicknesses.

PVA-based sheets can be realized in the form of solid films having a thickness of, for example, 30 to 50 μm, preferably about 35 μm.

Such sheets may advantageously have a gram weight of 20 g / m ² to 60 g / m ² , preferably 30 g / m ² to 50 g / m ² .

After application of the sheet, it has proved advantageous to perform planarization of the sheet against the mold surface to reduce or preferably remove any voids or bubbles present between the sheet and the lower mold surface.

Planarization is particularly advantageous when a subsequent vacuum vibration compression process is performed, since any bubbles present under the sheet will expand during the vacuum process resulting in separation of the film from the sheet. Advantageously, the planarization can be carried out by a direct mechanical action on the sheet or by a pneumatic action involving the suction of air between the sheet and the mold. In the first case, the planarization can advantageously be carried out by rolling or brushing, ie using a soft roller or brush which is transferred over the sheet, for example at a suitable pressure. This is advantageous for shallow mold parts such as mold covers.

In a second preferred case, for example, for a deeper mold portion, such as a tray or base of a mold containing a mixture, the sheet is sucked against the mold surface by suction of air between the mold and the sheet due to its expandable nature. Can be. In this case, the sheet is preferably pre-fixed to the mold along the peripheral edge as will be apparent below.

Advantageously, an adhesive fluid layer between at least some area of the mold and the sheet ensures proper proper adhesion of the sheet 15 to the mold surface. This attachment is useful for keeping the sheet in place and preventing the formation of folds or creases in the sheet during subsequent processing steps, but at the same time, as well as preventing the subsequent spontaneous separation of the sheet from the mold after formation of the slab, as will be apparent below. I never do that.

Indeed, very small amounts of aqueous flow agents form adhesives and result in partially limited dissolution of the solid PVA film surface, allowing for the necessary attachment to the lower surface of the rubberized mold. The small amount of water present in the adhesive is incorporated into the film structure.

The amount of flow agent is in any case small enough to avoid complete dissolution of the PVA film.

Thus, the fluid layer is incorporated into the structure of the PVA-based sheet, thus only ensuring the desired attachment to the mold without negatively affecting the latter.

It should also be noted that the use of flow adhesives composed of PVA solution allows the application to be carried out in very small amounts without the risk of leaving "patchy zones", ie areas not properly covered by the fluid.

The layer of adhesive ensures that the sheet is sufficiently attached to the mold, but nevertheless also ensures subsequent easy removal of the slab from the mold.

Advantageously, using PVA solution and PVA based sheet, they are completely removed from the slab simply by subsequent washing with water (also during conventional mechanical slab wet-polishing and finishing operations) or by mechanical peeling. It provides an advantage that can be made.

Instead, as conceived in accordance with the principles of the present invention, due to the adhesion of the sheet to the mold, there is no need for deep mechanical removal operations, so that there is no formation of creases or folds that can be incorporated into the slab forming mixture. To ensure that.

2 shows a schematic view of a plant for the preparation of a mold according to the invention by applying the method described above.

For simplicity of the following description, reference will be made to the preparation of the bottom or tray of the mold, but as will be apparent to one skilled in the art, for similar preparation of the top or cover of the mold, such an arrangement in an inverted position compared to that shown in FIG. The same plant can be used to insert the top into the plant. For convenience, reference will be generally made to the mold in any case below, without distinguishing between the bottom and top.

Obviously, the same plant can be used sequentially for the preparation of the top and bottom of the mold, or alternatively two plants can be used, ie one is intended for the top preparation and the other is the bottom of the mold. It is intended for the preparation of wealth.

As can be seen in FIG. 2, such a plant (typically denoted by 20) is intended for laminating a sheet of PVA-based plastic material and a first station 21 for applying a layer of fluid to a predetermined zone of the mold. A second station 22.

It is advantageous for the conveyor (preferably belt type) 23 to be arranged between the two stations, the conveyor running between and below the first station and the second station, so as to carry the mold sequentially to the two stations. Intended; Alternatively two stations can be displaced over the mold to remain fixed. That is, the station can also be designed to be mobile and can be placed over the mold instead of placing the mold under the station.

The planarization device can be arranged downstream of the sheet application zone.

For example, in the first embodiment according to the invention, by means of an accessory element, the planarization is such that the second station 22 performs mechanical planarization of the sheet 15 against the surface of the mold 10 upon delivery of the mold. Including or following device 24 may be advantageously contemplated.

The first station 21 is intended to evenly distribute the fluid layer on the predetermined surface of the mold passing below, with the surface to be carried by the conveyor 23 and directed upward to be treated. Application of the flow agent allows the sheet to be properly secured to the mold for subsequent process operation.

Advantageously, the first station 23 is an applicator element, immersed or coated with a fluid, to transfer the fluid by contact on the surface of the mold passing under it in the fluid discharge zone 26, 25).

In particular, a belt running between the fluid discharge zone 26 and the zone 28 for removing fluid supplied by the fluid reservoir (eg, a fluid tank (not shown)) in which the applicator element is immersed or coated with fluid. It has proved to be advantageous to include (27). The movement movement advantageously takes place in the direction of movement of the mold under the station.

The belt is made of a material suitable for absorbing and / or collecting an amount of fluid and transporting it to the discharge zone 26, where the fluid can be transported onto a desired area of the mold surface.

In a preferred embodiment, the belt 27 is wound around two rollers 29, 30 across the movement of the mold. The first roller 29 is positioned at the bottom such that the belt is positioned in the fluid discharge zone 26 where the belt is wound around and in contact with the desired portion of the mold surface to which the fluid is to be coated.

The second roller 30 is instead at least one section between the two rollers inclined toward the forward movement direction of the conveyor 23 in the top position and preferably on the upwardly directed side where the belt is designed to remove the fluid from the fluid reservoir. Is positioned to have. Before the moving belt 27 reaches the discharge zone, means for conveying the emulsion onto the belt to be applied to the mold are advantageously along the inclined section. Such means can be of various types as one of ordinary skill in the art can readily imagine.

For example, it has proven advantageous to use a third roller 31 parallel to the first two rollers arranged in contact with the upwardly directed side of the moving belt.

The three rollers and the belt can clearly extend transverse to the conveyor to cover the entire width of the mold surface to be treated.

As can be seen in FIG. 2, a removal zone 28 for injection of the fluid is formed between the belt and the third roller, which fluid accumulates between the belt and the third roller and towards the discharge zone 26. Delivered in small quantities by.

The third roller 31 is preferably arranged to counterrotate with respect to the belt 27 to facilitate adhesion of the fluid onto the belt.

The belt basically operates in the manner of a stamping machine which removes the fluid and dispenses it on the surface of the mold in contact with the belt in the discharge zone 26. Thus, the distribution of fluid occurs essentially by rolling or spawning.

The fluid application device can advantageously adjust the vertical position of the applicator element, for example, to allow passage of raised mold portions (e.g., the rim 13) and to not contaminate the portion that should not be coated with the fluid. A pneumatic piston 32 is provided to make it. For example, the device may be raised to avoid contaminating the conveyor when the mold is not under the station.

3 and 4 show the second station 22 and the flattening device 24 in more detail when present.

The second station 22 may comprise a discharging device capable of discharging a single sheet prepared in advance to the correct length. However, the sheet 15 is in the form of a continuous strip of film (indicated by 15b) which is unwound from the reel 33 having an axis below the ejection device across the direction of movement of the mold and then cut to size. It has proved to be advantageous to include a feeder device 16 that emits.

Preferably, the unwinding of the plastic film can be performed autonomously since the plastic film adheres to the surface of the mold due to the adhesive fluid just applied.

This ensures accurate application of the film, due to the slow feeding of the film, without excessively fast feeding, or wrinkles due to tearing or abrasion.

In particular, according to a possible structure of the plastic film feeder device, the plastic film 15b unrolled from the reel 33 extends the plastic film from one or more transfer rollers 34 to which the film follows and on the surface of the mold to which the film then contacts. It leads from the final roller 35 which has a function to make.

At least the final rollers 35 each press the lower conveyor 23 to press the film with an appropriate force against the surface to be covered and / or to allow the peripheral edge of the tray to pass through, as will be explained more fully below. It is movable vertically so that it can be moved towards or away from it.

To perform this vertical movement, as is clearly shown in FIG. 4, a pair of pneumatic pistons 36, 37 are provided.

Advantageously, on the reel 33 of the plastic film there may be additional rollers 38 which may preferably have a soft and brushed form, which rollers are elastically pushed about the periphery of the reel 33, In order to prevent or reduce the subsequent capture of bubbles between the sheet in the mold and the laminated surface and to prevent wrinkles of the sheet before being applied on the mold, it has the function of smoothing the plastic film, if necessary.

The roller 38 can also prevent the uncontrolled loosening of the reel to maintain the correct tension of the plastic film between the reel and subsequent rollers 34 and 35.

In order to carry out the cutting to the size of the film strip to form a sheet on the mold, a cutting device 39 is advantageously provided, which device is arranged across the unrolled film strip and advantageously of the roller 35 Located downstream.

In particular, it has proven advantageous to provide the cutting device 39 with a wire 40 which is heated to the temperature required to melt the material of the film and arranged across the feeding direction of the mold. The motor drive means 41 (e.g., one or more pneumatic pistons), when commanded, operates the wire 40 in a non-operating raised position that does not interfere with the plastic film and the wire is arranged relative to the plastic film, Move between lowered cutting positions. As can be seen in FIG. 4, the wire is advantageously located on the side of the conveyor 23, on which the two ends at which the motor drive means 41 operate via the connection and the connection devices 44 and 45. Supported and tensioned between (42, 43). The movement of the wire between the two non-operational positions and the operating position can be perpendicular such that the film descends onto the film once it is deposited on the mold.

Advantageously, the wire is metallic and heated by the Joule effect through the current flowing due to the power supply (not shown) connected to its two ends 42 and 43.

As can be clearly seen again in FIG. 3, the optional planarization device 24 (used for the mechanical planarization action in the first possible embodiment of the invention) is preferably across the direction of movement of the conveyor and towards the conveyor. It includes a pressure roller 46 having an axis of rotation that is pushed onto a sheet laminated on the mold surface and presses against the mold surface as it passes under it. This pushing action can be obtained, for example, by proper elastic support of the roller 46, the weight of the roller itself, the yielding design of the peripheral surface of the roller, or a combination of these three characteristics.

The press roller 46 may be made, for example, in the form of a soft or compressible peripheral surface or brush.

During use of the plant, the mold part (tray or cover) to be processed is moved on the conveyor 23 with the side to be processed being upwardly oriented as schematically shown in FIG. 2. As already mentioned, the figures associated with the plant show the bottom mold part or tray 11 for the sake of simplicity. Similar treatment may be applied to the top or cover 12 of the mold where the mixture should be closed inside the mold.

Initially, both the station 21 for applying a layer of fluid and the second station 22 for laminating a sheet of plastic material are in their stop position, ie the raised fluid applicator element 25. And plastic film supply devices, respectively.

When the front end of the mold (the front end and the rear end is understood with respect to the movement of the mold along the plant) reaches the first station 21, the fluid applicator element 25 is lowered to the bottom of the mold to be treated with the fluid. It comes into contact with the surface.

5 shows a possible first application procedure according to the invention. According to this first procedure, the applicator element 25 is lowered so as to substantially contact the entire surface of the mold which will later receive the sheet (avoid only the rim of the tray 11 if necessary). In particular, the fluid is applied on the bottom of the mold.

The forward movement of the mold allows the stack of desired fluid layers to be processed over the entire surface of the mold, as can be seen clearly in FIG. The rear end of the mold is raised when passed by the applicator element 25 and the application of the fluid is finished.

When the front end of the mold reaches the second station 22, the device for supplying the plastic film 16 is operated to start dispensing the plastic sheet. In particular, for the plant shown in FIG. 6, the roller 35 is lowered such that the front end of the plastic film is pushed towards the surface of the mold covered with the fluid.

In this condition, as can be clearly seen in FIG. 6, the forward movement of the mold allows the film to be transferred and laminated on the mold surface. The rear end of the mold is raised when passed by the roller 35 and the application of the film is finished.

As can be seen again in FIG. 6, where the flattening device 24 is present, it is operated to cause the plastic film to adhere to the surface of the mold to prevent trapping of bubbles.

As can be seen in FIG. 7, when the application of the plastic film is complete, the roller 35 is raised and held in this position. Instead, the cutting device 39 is operated to cut and separate portions of the film dispensed on the mold, creating a new shear for the next dispensing action that occurs upon arrival of a new mold. Instead, the flattening device continues its action and completes the operation.

As already mentioned above, the application of fluid over the entire surface of the mold to be covered by the sheet is preferred in the case of shallow molds. For example, the procedure described above can advantageously be used to cover the cover of the mold.

For deeper molds, pure mechanical application of the sheet may not always be satisfactory.

In this case, it has proved advantageous to perform "pneumatic" planarization of the sheet, using a planarization device arranged downstream of the sheet application zone and operating by a vacuum system instead of the system having the mechanical device 24 described above.

In the case of a vacuum planarization action, it has also turned out to be advantageous if the fluid is applied only on some areas of the mold surfaces which should be covered by the sheet.

In particular, it has proven advantageous to apply fluid only to the peripheral areas of the mold to define a central area where air can be inhaled.

This variant of the method according to the invention is shown by way of example in FIG. 8.

According to this variant, when the front end of the mold reaches the first station 21, the fluid applicator element 25 is lowered to contact only the peripheral edge or rim of the mold. In this way, in the first operating station, the PVA-based adhesive is dispensed using the method already described above, but only on the top peripheral edge (eg tray) of the mold.

As can be clearly seen in FIG. 9, the mold thus processed is then moved to a sheet application station 22 so that the sheet is stretched on the mold to attach to the peripheral edge of the mold treated with the adhesive fluid. In this way, the sheet is kept horizontal and arranged away from the bottom of the mold and, due to the PVA-based adhesive and its lightness, remains completely in place (like the skin of the drum) on the mold die cavity.

At station 22, the optional planarization device 24 is not used (thus, as can be seen from FIG. 9, also may not be present). Instead, if air intake is subsequently used, this is advantageously done through a suction duct arranged in the mold to protrude inside the mold defined by the peripheral edge of the mold. Thus, the suction means will be provided instead of the flattening device 24.

In particular, the mold 11 with the applied sheet can be transferred to a subsequent station 50, referred to as the mixture dispensing and diffusion station, shown schematically in the top view of FIG. 10 and in the cross-sectional view of FIG. 11.

In such a station the mixture is typically injected into a mold, and the station is typically used to move the mold 11 against a known dispensing unit 52 which can dispense the mixture in the correct amount within the mold. (Eg, known belt conveyors). When the solid film is positioned inside the mold according to the first embodiment of the present invention, the station 50 will be of a substantially known type, as can be easily imagined by those skilled in the art.

The mixture is generally injected into the mold by the longitudinal movement of the mold and dispensing unit 52, the dispensing unit extending transversely over the entire width of the mold. Relative movement relative to the dispensing unit and the mold is known per se and thus will not be further illustrated or described herein, and can be easily imagined by those skilled in the art.

Preferably, this will be a unit 52 that moves along the mold held stationary inside the station 50. However, movement of the mold under unit 52 that remains stationary or combined movement of the mold and the unit may also be used as desired.

Dispensing will advantageously be performed by a known " loose " action in which the mixture is diffused to flatten the free surface of the mixture inside the mold. According to the invention, before injection of the mixture, planarization of the sheet arranged on the mold is carried out during the steps already described above.

As shown in FIG. 9, if the film is fixed on the top peripheral edge of the mold and has not yet been flattened, there is a vacuum flattening or stretching device 53 directly in the station 50, prior to and in some cases dispensing of the mixture. It is also possible to carry out the planarization / extension step by suction of air trapped between the sheet and the mold during that time.

For this purpose, the diffusion station 50 advantageously comprises suction means which form a vacuum planarizing device 53 and which are suitably connected to the mold 11 reaching the station. Air can be removed.

In particular, the suction means can be arranged in the station 50 along the peripheral edge of the mold to link (connect) with a suitable suction duct (eg, a duct having a diameter of about 6 to 10 mm) present in the mold and Under the sheet 15, the inner cavity of the mold is connected to the outside of the mold.

Advantageously, the edge of the mold on which the suction means is arranged can be two opposing longitudinal edges such that the mold can be arranged between the suction means 53 by the same conveying movement of bringing the mold into the station 50. .

The passages and associated suction means within the mold can advantageously be arranged at intervals along the edge of the mold to uniformly suck the trapped air under the sheet applied to the mold, as is clearly visible in FIG. 10. For example, the suction means can be formed by four connectors on one side of the mold and four connectors on the opposite side.

Again advantageously, the bottom of the mold may preferably have a surface that is not smooth to allow better discharge of air between the bottom of the mold and the solid PVA film. To achieve this, the rubber side of the mold, in which the mixture is laminated with the PVA sheet in between, instead of smooth, may have a suitable surface roughness, which is preferably a surface cloth, for example with knurled imprints or the like. Or by using rubber.

Because of the roughness of the inner surface of the mold, microchannels are created for the passage of air, which allows air to be sucked into the center of the mold (or tray) as well as close to the edge of the mold, so that the solid PVA film may It rests perfectly over the bottom of the tray without the risk of causing puckering.

Also, if the inner surface of the mold is made of cloth, the PVA film adheres better to the bottom of the tray because the cloth has better grip properties than rubber.

FIG. 12 shows an enlarged view of an advantageous embodiment of the suction means (in the area indicated by the dashed circle in FIG. 11) designed to allow automatic control engagement with the aforementioned suction duct present in the mold.

As can be seen in FIG. 12, the suction duct (generally designated 54) preferably extends laterally in the mold's inner cavity close to the bottom, thus allowing the PVA sheet to move towards the bottom of the mold. Allow accurate air intake even when starting.

Again in FIG. 12, the suction means 53 is pushed against each end duct 54 against the end of the duct 54 protruding out of the mold by a suitable actuator 56 (eg pneumatic actuator). It is understood that the method can include a sealed connecting end 55 (eg in the form of a suction cup). Advantageously, the actuator 56 advances the sealed connecting end 55 to the retracted position shown by the solid line in FIG. 12 and the dashed line in FIG. 12 to form a seal about the outer end of the duct 54. Move horizontally between the operating positions.

The connecting end 55 is then connected to a controlled vacuum source or vacuum plant (not shown) to draw air into the interior cavity of the mold through the passage 54. Advantageously, at the end of the duct 54 opening into the mold, a suitable filter 57 is provided which allows air to pass but for example prevents the sheet 50 from being sucked into the duct 54.

During operation of the plant, when the mold (prepared as described with reference to FIGS. 8 and 9) reaches the diffusion station 50, the suction means 53 is connected to a duct 54 present in the mold and , To inhale air between the bottom of the mold (eg, in the form of a tray) and the solid film 15 applied to the edge of the mold.

As a result, as shown by dashed lines in FIG. 12, to assume the final shape, the solid film due to its expandable nature is stretched and seated against the inner surface of the rim and the bottom of the mold.

The suction time required for the solid film to be perfectly aligned with respect to the inner surface of the mold can be shortened to only a few seconds. However, for greater reliability, inhalation can be maintained for longer periods before injecting the mixture. In addition, suction can also be maintained during the entire mixture dispensing and diffusion operation to ensure that the sheet 15 remains stable against the bottom of the mold.

Once the mixture has been injected, the air intake can be stopped because the film previously formed by inhalation acts on the weight of the mixture dispensed thereon, thus maintaining the form attached to the surface of the mold.

In addition, the diffusion station 50 may preferably comprise a peripheral rim 58 for containing the mixture, which is lowered by the frame 59 through the drive means (not shown) and the mixture is injected. Is placed on the bottom of the tray before its peripheral edge. The rim is shown, for example, in the raised position in FIG. 11 and in the lowered position in the mold in the enlarged view of FIG. 13. The rim may also form part of the dispensing unit 52 to move with it at least vertically.

The function of the peripheral rim helps to include the mixture when the mixture is dispensed inside the tray and prevents some of it from accidentally spilling out of the tray.

Once the containment edge is lowered, air intake is still activated and the mixture is dispensed into the tray. Once the dispensing of the mixture is complete, the perimeter including the rim can be raised again and the mold separated from the suction means can be transferred for subsequent slab generation steps.

In either case, once the mold is filled with the mixture, it can be closed at the top with a suitable cover, which has been advantageously pre-treated with the applied PVA film, for example, as already described above. For example, a closed station (substantially known per se and thus not shown) may pick up the cover, turn it over and stack it on top of the mixture contained within the tray.

The tray thus closed and containing the mixture can then be transferred to a forming station (also known per se and thus not shown), where preferably a known step of vacuum vibrating of the mixture is carried out.

The internal filter 57 present inside the duct 54 of the mold also creates protrusions that will prevent the mixture from being pushed into the passage during vibrational compression, tearing the PVA film and / or extracting the slab from the tray after curing. It has a function to prevent it.

At the end of the production line, the cover can be finally removed to remove the hardened slab. In addition, return lines for covers and trays can be provided that can be cleaned and then used again for application of the solid PVA film, as previously described, the mold preparation and slab generation cycles are repeated. .

The slab may be conveyed after catalysis and curing, instead, for removal of the PVA sheet. The sheet can be peeled off mechanically (using a manual or automatic device) from the slab, or the slab can still be transferred to the wet polishing and sizing line to which the sheet is applied, where the process water is subsequently removed along with the process sludge. Resulting in dissolution of the sheet.

At this point, it is clear how the predefined object has been achieved. Due to the principles of the present invention, the surface of the mold is adequately protected, the resulting slab can be easily separated from the mold, and sufficient adhesion of the protective sheet to the mold is ensured during the preparation and use of the mold.

Apparently, the foregoing description of the embodiments applying the innovative principles of the present invention is provided as an example of such innovative principles, and therefore should not be taken as limiting the scope of the claims claimed herein.

For example, depending on the length of the mold and the distance between the stations, applying the fluid layer and stacking the solid layer may include the sheet lamination station on the front of the mold while the fluid application station is operating on the back of the mold. You can temporarily completely separate or partially overlap in that it is already working.

In either case, once lamination and any planarization is complete, the mold may leave the preparation plant and also continue subsequent slab manufacturing steps if necessary after the temporary storage period.

As mentioned above, during the subsequent steps, preferably the mixture of aggregates forming the slab will be dispensed in the mold, and the mold is closed with a cover at the top if necessary; Slab will be formed; The slab is allowed to undergo a curing process; The slab is extracted from the mold together with the sheet or sheets; The sheet is removed from the slab.

The molding process may then optionally include known procedures for vibrational compression under vacuum and subsequent compression by hot curing of the mixture. Removal of the sheet can be carried out mechanically and / or by dissolving the sheet in water (e.g., during a mechanical process for finishing the slab surface generally comprising wet-polishing and sizing).

All such subsequent process stages are known per se and are not shown or described in more detail here as they can be readily imagined by those skilled in the art in view of the description provided herein.

In accordance with the principles of the present invention, a rubber tray can be used with all associated advantages and it is ensured that no part or trace of the protective sheet is trapped and retained in the slab even when the mixture is subjected to vibrational compression.

Thus, during sizing and smoothing of the hardened slab, the material of thickness, whether or not to be removed, will be smaller in nature.

As a result, the thickness of the mixture layer to be dispensed inside the tray can be reduced, and thus the amount of mixture strictly required for each slab can be used.

There is also a reduction in the amount of sludge treatment as well as a reduction in the cost and energy costs of the tools required for the treatment of the slab.

In order to obtain a more uniform release of the fluid layer and greater control over its small thickness, application of the fluid has proved to be desirable, in particular by contact with a device having the applicator element described above, The first station 21 may also alternatively comprise a suitable nozzle located in the fluid discharge zone for spraying the fluid directly towards the surface of the mold passing through the zone. In addition, other known contact application elements and devices can be used.

The application of the fluid and the application of the sheet between the mold and the sheet can also be carried out in much shorter time intervals and in much smaller spaces than those shown and described. For example, the fluid may be applied directly at the sheet stacking station just before contacting the mold surface to which the sheet is to be attached, arranged between the sheet and the mold surface, and not necessarily spreading over the mold surface beforehand.

The shape, dimensions and proportions of the various parts of the mold and plant may differ from those shown here depending on the particular requirements. The plant may also include known accessory elements for its management, synchronization of operations, direction of passage of the mold part for activation of various mechanisms, and the like.

In order to protect a very wide mold, two or more rolls of solid films arranged in parallel can also be used so that the film of each roll can cover only a part of the surface of the mold. This may be useful, for example, when a slab of considerable width must be produced.

Claims (24)

As a method for the production of slabs from a mixture of aggregates,
Preparing a mold 10 intended to form a slab from a mixture of agglomerates, wherein at least one sheet of PVA-based plastic material 15 is formed to form a surface for subsequent contact with the mixture to be introduced into the mold. Laminating over the surface of the mold, interposing a layer (14) of fluid agent comprising PVA in solution between the sheet (15) and at least some region of the mold surface. The method of claim 1,
After lamination of the sheet 15 on the surface of the mold 10 with the layer of fluid 14 interposed thereon, the step of flattening or stretching the sheet 15 with respect to the mold surface is carried out. How to. The method of claim 2,
Said flattening or stretching step occurs at least in part by a mechanical action on said sheet (15). The method of claim 2,
Said flattening or stretching step occurs at least in part by suction of air between said sheet (15) and said mold (10). The method of claim 4, wherein
The mold 10 comprises a peripheral edge 13 of the mold and the suction of air is present along the peripheral edge of the mold to protrude inside the mold defined by the peripheral edge 13. And 54 through. The method of claim 4, wherein
Said inhalation occurs before or during the dispensing step of said mixture within said mold. The method of claim 1,
And wherein said layer of fluidizing agent is applied by mechanical contact with an applicator element soaked or coated with said fluidizing agent. The method of claim 1,
The flow agent comprises an aqueous solution and optionally PVA in glycerin. The method of claim 1,
The average amount of applied flow agent is 2 g / m ² to 10 g / m ² ,
Said sheet of PVA-based plastic material has a gram weight of 20 g / m ² to 60 g / m ² . The method of claim 1,
Wherein the mold (10) is a mold or flexible sheath made of an elastomeric material or cloth. The method of claim 2,
The mold 10 includes a tray-shaped base portion and a cover portion to be overlapped on the base portion,
The step of planarizing the PVA sheet 15 in the base portion is caused by the suction of air between the sheet and the mold
Planarizing the PVA sheet at the cover portion occurs by mechanical action on the sheet. The method according to any one of claims 1 to 11,
Introducing a mixture of the aggregates forming the slab into the mold (10) having at least one sheet of PVA-based plastic material (15) previously stacked inside the mold;
Performing a slab forming process having a compression step by vacuum vibration compression;
Performing a curing process of the slab to consolidate the slab;
Extracting the slab from the mold (10) together with the sheet;
Removing the sheet from the slab with dissolving the sheet made of soluble material in water. 12. A system comprising a plant (20) for performing the steps of the method according to any one of claims 1 to 11.
Flow agents comprising PVA in solution;
At least one sheet of PVA-based plastic material;
The plant is sequentially
A first station (21) for application of the layer of fluid (14) comprising PVA in solution on at least some areas of the surface of the mold; And
A second station (22) for lamination of the sheet of PVA-based plastic material (15) on the layer. The method of claim 13,
The first station 21 comprises an applicator element 25 immersed or coated with the flow agent, to contact on the mold surface through the zone 26 for the discharge of the fluid of the applicator element 25. System for conveying the fluid. The method of claim 14,
The applicator element (25) is characterized in that it comprises a belt running between the zone (28) for removal of the fluid and the zone (26) for discharging the fluid to be immersed or coated with the fluid. The method of claim 13,
The second station transversely cuts the strip of film to form the sheet and the devices 33, 34, 35 for ejecting the sheet in the form of a strip of film 15b released from the reel 33. A device (39) for use. The method of claim 13,
The second station (22) comprises or follows a planarization device (24, 53) for smoothing the sheet with respect to the mold surface. The method of claim 17,
The planarization device (24) is characterized in that it comprises a pressure roller (46) having an axis of rotation transverse to the direction of movement on the mold and being pushed to act on the sheet present on the surface of the mold. The method of claim 17,
Said planarization device comprises suction means (53) for sucking air between said sheet and said mold. The method of claim 19,
The suction means 53 is arranged in a station 50 for dispensing and diffusing the mixture in the mold, and is movable in order to connect / disconnect to the suction duct 54 present in the mold. System. As mold 10 intended to form a slab from a mixture of aggregates,
With the base portion 11 and the mixture introduced into the mold to form a slab between the sheet 15 and at least some region of the inner surface of the mold 10 in which the layer 14 of PVA-comprising adhesive is present. And a cover (12) having an inner surface of said mold covered with at least one sheet of PVA-based plastic material (15) to form a surface intended for subsequent contact. The method of claim 21,
A suction duct (54) intended to connect a defined / included space between the mold surface and the sheet to an external suction means for flattening or stretching the sheet with respect to the mold surface by vacuum. The method of claim 22,
The suction duct (54) is characterized in that it comprises a filter (57) arranged at one end of the duct leading to the mold. The method of claim 21,
The inner surface of the mold is at least partially made of a cloth or rubber having a knurled surface.

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